Synthesis and structural characterization of five-coordinate aluminum complexes containing diarylamido diphosphine ligands

Article abstract of DOI:10.1021/ic802030d

A series of five-coordinate aluminum complexes supported by o-phenylene-derived amido diphosphine ligands, [N(o-C₆H ₄PR₂)₂]^- ([R·PNP] ^-; R = Ph, ⁱPr) and [N(o-C₆H

Full text of DOI:10.1021/ic802030d

5480 Inorg. Chem. 2009, 48, 5480–5487
DOI: 10.1021/ic802030d
Synthesis and Structural Characterization of Five-Coordinate Aluminum
Complexes Containing Diarylamido Diphosphine Ligands
Pei-Ying Lee and Lan-Chang Liang*
Department of Chemistry and Center for Nanoscience & Nanotechnology, National Sun Yat-sen University,
Kaohsiung 80424, Taiwan
Received October 28, 2008
A series of five-coordinate aluminum complexes supported by o-phenylene-derived amido diphosphine ligands,
i
[N(o-C6H4PR2)2]- ([R-PNP]-; R = Ph, Pr) and [N(o- C6H4PPh2)(o-C6H4PiPr2)]- ([Ph-PNP-iPr]-), have been
prepared and structurally characterized. Alkane elimination reactions of trialkylaluminum with H[Ph-PNP] (1a),
H[iPr-PNP] (1b), and H[Ph-PNP-iPr] (1c) in toluene at -35 °C respectively produced the corresponding dialkyl
i
complexes [Ph-PNP]AlR2, [iPr-PNP]AlR2, and [Ph-PNP-iPr]AlR2 (R = Me (2a-c), Et (3a-c), Bu (4a-c)) in high
isolated yield. The dihydride complexes [Ph-PNP]AlH2 (6a), [iPr- PNP]AlH2 (6b), and [Ph-PNP-iPr]AlH2 (6c) were
prepared in one-pot reactions of in situ prepared dichloride precursors (5a-c) with LiAlH4 in THF at room temperature.
X-ray diffraction studies of 2a-c, 3b-c, 5b, and 6b revealed a distorted trigonal-bipyramidal structure for these
molecules in which the two phosphorus donors are mutually trans. The solution structures of these organoaluminum
complexes were all characterized by 1H, 13C, and 31P NMR spectroscopy. The NMR data are indicative of solution C2
symmetry for [Ph-PNP]- and [iPr-PNP]- complexes, whereas they are indicative of C1 for [Ph-PNP-iPr]- derivatives.
The 1H NMR spectra of 3a-c and 4a-c revealed diastereotopy for the R-hydrogen atoms in these molecules.
Introduction
remain relatively unexplored.13-15 In this regard, we have
recently prepared a series of mononuclear aluminum com-
plexes of bidentate [NP]- and tridentate [PNN]- ligands
(Figure 1) that are amido phosphine derivatives.16,17 Though
available, examples of aluminum complexes containing tri-
dentate amido phosphine ligands are extremely rare.13,17
Pioneering work by Fryzuk and co-workers revealed that
phosphine dissociation from certain silyl-derived AlX2[N
(SiMe2CH2PiPr2)2] complexes may become facile, thereby
leading to the formation of four- instead of five-coordinate
species.13
Recent studies on aluminum chemistry have been focused,
at least in part, on the search for appropriate ancillary ligands
for reactive organoaluminum species due to their increasing
role in catalytic polymerization reactions.1 Much attention
has been paid to chelating systems that contain exclusively
hard donor atoms.2-12 Studies involving hybrid chelating
ligands incorporating both hard and soft donors, however,
*To whom correspondence should be addressed. E-mail: lcliang@mail.
nsysu.edu.tw.
(1) Coles, M. P.; Jordan, R. F. J. Am. Chem. Soc. 1997, 119, 8125–8126.
(2) Dagorne, S.; Atwood, D. A. Chem. Rev. 2008, 108, 4037–4071.
(3) Zhu, H.; Chen, E. Y.-X. Inorg. Chem. 2007, 46, 1481–1487.
(4) Zhao, J.; Song, H.; Cui, C. Organometallics 2007, 26, 1947–1954.
(5) Bai, G.; Singh, S.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H. G. J.
Am. Chem. Soc. 2005, 127, 3449–3455.
(6) Hormnirun, P.; Marshall, E. L.; Gibson, V. C.; White, A. J. P.;
Williams, D. J. J. Am. Chem. Soc. 2004, 126, 2688–2689.
(7) Liang, L.-C.; Yang, C.-W.; Chiang, M. Y.; Hung, C.-H.; Lee, P.-Y. J.
Organomet. Chem. 2003, 679, 135–142.
We have recently shown that incorporation of a relatively
rigido-phenylenebackbone inthe amido diphosphine ligands
may inhibit phosphine dissociation, at least to some degree,
and thus effectively increase the thermal stability of the
derived metal complexes.18-23 It has also been demonstrated
(15) Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G.
Organometallics 1998, 17, 4042–4048.
(16) Liang, L.-C.; Huang, M.-H.; Hung, C.-H. Inorg. Chem. 2004, 43,
(8) Yu, R.-C.; Hung, C.-H.; Huang, J.-H.; Lee, H.-Y.; Chen, J.-T. Inorg.
Chem. 2002, 41, 6450–6455.
2166–2174.
(9) Schmidt, J. A. R.; Arnold, J. Organometallics 2002, 21, 2306–2313.
(10) Korolev, A. V.; Ihara, E.; Guzei, I. A.; Young, V. G.; Jordan, R. F. J.
Am. Chem. Soc. 2001, 123, 8291–8309.
(11) Cosledan, F.; Hitchcock, P. B.; Lappert, M. F. Chem. Commun. 1999,
705–706.
(12) Qian, B. X.; Ward, D. L.; Smith, M. R. Organometallics 1998, 17,
3070–3076.
(17) Lee, W.-Y.; Liang, L.-C. Dalton Trans. 2005, 1952–1956.
(18) Liang, L.-C. Coord. Chem. Rev. 2006, 250, 1152–1177.
(19) Liang, L.-C.; Chien, P.-S.; Lin, J.-M.; Huang, M.-H.; Huang, Y.-L.;
Liao, J.-H. Organometallics 2006, 25, 1399–1411.
(20) Liang, L.-C.; Lin, J.-M.; Lee, W.-Y. Chem. Commun. 2005, 2462–
2464.
(21) Liang, L.-C.; Chien, P.-S.; Huang, M.-H. Organometallics 2005, 24,
(13) Fryzuk, M. D.; Giesbrecht, G. R.; Olovsson, G.; Rettig, S. J.
353–357.
Organometallics 1996, 15, 4832–4841.
(14) Fryzuk, M. D.; Giesbrecht, G. R.; Rettig, S. J. Inorg. Chem. 1998, 37,
6928–6934.
(22) Huang, M.-H.; Liang, L.-C. Organometallics 2004, 23, 2813–2816.
(23) Liang, L.-C.; Lin, J.-M.; Hung, C.-H. Organometallics 2003, 22,
3007–3009.
r
2009 American Chemical Society
pubs.acs.org/IC
Published on Web 04/28/2009

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5481
Scheme 1
Figure 1. Representative chelating amido phosphine ligands.
that the reactivity of these diarylamido diphosphine com-
plexes is a function of electronic and steric characteristics of
substituents at the phosphorus donors.24-26 For instance,
the reactivity of unsymmetrically substituted nickel
31P{1H} NMR spectra. In an independent experiment, 5b
was isolated in 76% yield as colorless crystals suitable for
X-ray diffraction analysis. Subsequent reactions of 5a-c
with LiAlH4 in THF at room temperature afforded [Ph-
PNP]AlH2 (6a), [iPr-PNP]AlH2 (6b), and [Ph-PNP-iPr]
AlH2 (6c), respectively, in high overall isolated yields.
In general, complexes 2-6 are thermally stable but extre-
mely sensitive to moisture. Compounds similar to 2b, 4b,
and 5b but derived from a tolyl backbone were prepared
similarly.27
Solution NMR Studies of Symmetrically Substituted
2a-6a and 2b-6b. The solution NMR data are all con-
sistent with a C2-symmetric, five-coordinate structure for
these aluminum complexes, in which the tridentate amido
diphosphine ligand adopts a meridional coordination
mode. Selected data are summarized in Table S1 (Sup-
porting Information). The 31P{1H} NMR spectra exhibit
a singlet resonance with chemical shifts relatively
upfield28 as compared to those of the corresponding
protio ligands (1a, -18.6 ppm; 1b, -13.3 ppm).19,23 An
upfield change in the 31P chemical shift is also observed
for [NP]-- and [PNN]--derived16,17 or other phosphine
coordinated aluminum complexes.13,14,29-31 The two
aluminum-bound alkyl (2a-4a and 2b-4b) or hydride
(6a-b) ligands are chemically equivalent. Both phos-
phorus donors in these organoaluminum species are
bound to the aluminum center, as evidenced by the triplet
resonances observed for the R-carbon atoms in the
13C{1H} NMR spectra. In general, the 13C chemical shifts
of R-carbons in [iPr-PNP]- derivatives are relatively down-
field as compared to those of [Ph-PNP]- analogues due
to bulkier and more electron-releasing properties of the pho-
sphorus substituents in the former.29,32-34 A similar
hydride complex [Ph-PNPiPr]NiH ([Ph-PNP-iPr]-
=
[N(o-C6H4PPh2)(o-C6H4PiPr2)]-) with respect to olefin in-
sertion is inferior to that of symmetrically substituted [Ph-
PNP]NiH ([Ph-PNP]- = [N(o-C6H4PPh2)2]-) but superior
to that of [iPr-PNP]NiH.25 In an effort to expand the territory
of aluminum chemistry and evaluate the possibility of cata-
lytic polymerization thereafter, we have set out to prepare a
series of diarylamido diphosphine complexes of aluminum.
In this contribution, we aim to illustrate the coordination
chemistry of these aluminum species, taking advantage of the
rigidity imposed by the o-phenylene backbone. In accord
with a computational study on related species that contain a
tolyl-derived ligand,27 the solution NMR spectroscopic and
X-ray crystallographic data reported herein are all indicative
of a five-coordinate structure for these aluminum complexes.
Results and Discussion
Syntheses. Alkane elimination reactions of H[Ph-
PNP]19,23 (1a) with AlR3 in toluene at -35 °C produced
the corresponding dialkyl complexes [Ph-PNP]-
i
AlR2 (R = Me (2a), Et (3a), Bu (4a)) in high isolated
yields (Scheme 1). Analogous reactions employing
H[iPr- PNP]19 (1b) or H[Ph-PNP-iPr]25 (1c) gave
[iPr-PNP]AlR2 (2b-4b) and [Ph-PNP-iPr]AlR2 (2c-4c),
respectively. These organoaluminum complexes were all
isolated as colorless or pale-yellow crystals following
standard workup procedures. Interestingly, no THF
or Et2O adduct was formed in spite of the employment
of these ethereal solvents in crystallization, consistent
with the prediction that phosphine dissociation is not
significant.18-23,27
Preparation of dihydride complexes was also achieved.
The presumed dichloride precursors 5a-c may be pre-
paredinsitueitherfrom the metathetical reactions of AlCl3
with the corresponding lithium complexes of the amido
diphosphine ligands in THF at -35 °C or by the treatment
of MeAlCl2 with the corresponding protio ligands in
toluene at -35 °C. Though not isolated, complexes 5a-c
are likely produced quantitatively, as evidenced by
(28) The factors responsible for the upfield shift of 31P resonances of these
species are not clear at this stage. It has been argued (for instance, see ref 29)
that a decrease in C-P-C angles upon phosphine coordination to aluminum
would give a more negative 31P shift, but this study shows clearly a reverse
trend (see Tables S3 and S4 in the Supporting Information). The difference in
electronegativity in the M-P bond and the change in the π-electron overlap
seem not to correlate well either, in comparison of the data reported herein
with those of group 10 metal and lithium derivatives (refs 19-20, 22-23).
(29) Barron, A. R. J. Chem. Soc., Dalton Trans. 1988, 3047–3050.
(30) Muller, G.; Lachmann, J.; Rufinska, A. Organometallics 1992, 11,
2970–2972.
(24) Liang, L.-C.; Chien, P.-S.; Lee, P.-Y.; Lin, J.-M.; Huang, Y.-L.
Dalton Trans. 2008, 3320–3327.
(25) Liang, L.-C.; Chien, P.-S.; Lee, P.-Y. Organometallics 2008, 27,
(31) Barron, A. R. Organometallics 1995, 14, 3581–3583.
(32) Healy, M. D.; Ziller, J. W.; Barron, A. R. Organometallics 1991, 10,
597–608.
3082–3093.
(26) Liang, L.-C.; Chien, P.-S.; Huang, Y.-L. J. Am. Chem. Soc. 2006,
128, 15562–15563.
(33) Power, M. B.; Bott, S. G.; Atwood, J. L.; Barron, A. R. J. Am. Chem.
Soc. 1990, 112, 3446–3451.
(27) DeMott, J. C.; Guo, C.; Foxman, B. M.; Yandulov, D. V.; Ozerov,
O. V. Mendeleev Commun. 2007, 17, 63–65.
(34) Power, M. B.; Bott, S. G.; Clark, D. L.; Atwood, J. L.; Barron, A. R.
Organometallics 1990, 9, 3086–3097.

5482 Inorganic Chemistry, Vol. 48, No. 12, 2009
Lee and Liang
dependence on the steric nature of aluminum-bound
alkyls is also observed; that is, the larger isobutyl in 4
gives more downfield shifts for R-carbon resonances than
ethyl in 3 or methyl in 2.
Scheme 2
The solution C2 symmetry observed for 2a-6a and
2b-6b is notably different from the C2v symmetry found
for the group 10 complexes19,20,22-26 of these amido
diphosphine ligands due to the presence of time-averaged
symmetry planes in the latter, as evidenced by solution
NMR data. Such a discrepancy is presumably ascribable
to a slower exchange rate for aluminum species in a
“flipping”35-37 process involving two o-phenylene rings,
as illustrated in Scheme 2. The steric repulsion between
two CH moieties ortho to the amido nitrogen donor in the
C2v form is likely too much for M = Al to overcome the
exchange barrier. A variable-temperature 1H NMR study
of 2b in toluene-d8 (60 mM) revealed that the two
isopropylmethine resonances do not tend to coalesce even
at 90 °C, suggesting a significant exchange barrier for the
proposed flipping process in this molecule.
steric repulsion between the phosphorus substituents and
two aluminum-bound anionic ligands than that arising
from one nickel-bound ligand due to distinct coordina-
1
tion geometries. The H and 13C{1H} NMR spectra of
2c-6c exhibit two sets of resonances for the PiPr2 moiety,
indicating the absence of a symmetry plane in these
molecules. Consistently, the aluminum-bound alkyls in
2c-4c are chemically inequivalent. The hydride ligands in
6c display a broad singlet resonance at 5.25 ppm (Δν1/2
=
Interestingly, among the compounds investigated,
complexes 3b and 4b exhibit two well-resolved multiplet
resonances for the R-hydrogen atoms (Figure S1e,f, Sup-
porting Information), consistent with the anticipated
diastereotopic characteristic. The chemical nonequiva-
lence of the R-hydrogen atoms in AlCH2R (R = H (2a,b),
Me (3a,b), i-Pr (4a,b)) fragments is ascribable to the lack
of symmetry in these molecules with respect to internal
rotation involving the Al-CR bonds.38 With less sterically
demanding hydrocarbyl groups incorporated (e.g., phos-
phorusbound phenyl in 2a-4a or aluminum-bound
methyl in 2a and 2b), rapid rotation about the Al-CR
bonds becomes facile, and thus the diastereotopic R-
hydrogen atoms are indistinguishable on the NMR time
scale.
80 Hz) due likely to the fast relaxation of quadrupolar
aluminum atoms (27Al, I = 5/2, 100% natural abun-
dance).39,40 As anticipated, the R-hydrogen atoms in 3c
and 4c are diastereotopic, as evidenced by the 1H NMR
spectra (Figure S1h,i, Supporting Information).
X-Ray Studies. X-ray diffraction studies of 2a, 2b, 2c,
3b, 3c, 5b, and 6b established the solid-state structures of
these dialkyl, dichloride, and dihydride complexes. Crys-
tallographic data are given in Table 1. Selected bond
distances and angles are summarized in Tables 2 and 3,
respectively. As depicted in Figures S2-S4 (Supporting
Information), the coordination geometry of these mole-
cules is best described as a distorted trigonal bipyramid
with the two phosphorus donors being at the axial posi-
tions, consistent with that established by solution NMR
spectroscopy. The aluminum center lies perfectly on the
equatorial plane defined by the amido nitrogen and the
two anionic, monodentate ligands as evidenced by the
sum (ca. 360°) of the bond angles involving these equa-
torial donors. The C-Al-C angles in the dialkyl 2a, 2b,
2c, 3b, and 3c are generally close to the ideal value of 120°
for a trigonal-bipyramidal structure, but the Cl-Al-Cl
angle in 5b is relatively sharp, as anticipated from the
standpoint of the higher electronegativity of Cl (3.16)
than that of C (2.55). 41 Consistently, the Al-P distances
of dichloride 5b are significantly shorter than those of
dialkyls.27 In unsymmetrically substituted 2c and 3c, the
Al-P distance corresponding to the isopropyl substituted
Solution NMR Studies of Unsymmetrically Substituted
2c-6c. With the incorporation of the unsymmetrically
substituted [Ph-PNP-iPr]- ligand, complexes 2c-6c are
C1-symmetric on the NMR time scale. The 31P{1H} NMR
spectra of these species exhibit two doublet resonances,
consistent with concomitant coordination of the two
distinct phosphorus donors to the aluminum center.
Reminiscent of what has been found for the symmetri-
cally substituted counterparts, the 31P chemical shifts of
2c-6c are relatively upfield28 as compared to those of 1c
2
(-14.8 for PiPr2 and -16.7 ppm for PPh2).25 The JPP
coupling constants of 9 Hz for 2c-4c and ca. 49 Hz for
5c-6c are notably smaller than those found for the four-
coordinate divalent nickel species such as [Ph-PNP-iPr]
NiH (244 Hz),25 [Ph-PNP-iPr]NiEt (271 Hz),25 and [Ph-
PNP-iPr]Ni(n-hexyl) (273 Hz).25 Such discrepancy is per-
haps a consequence of smaller P-M-P angles for the
five-coordinate aluminum species than for the four-
coordinate nickel derivatives. The decreased P-M-P
angles for the former appear to reflect somewhat greater
˚
˚
arm (2c, 2.5499(18) A; 3c, 2.5700(13) A) is notably shorter
˚
than that involving phenyl (2c, 2.7902(17) A; 3c, 2.8038
˚
(13) A), in agreement with the anticipated electron-
releasing properties of these phosphorus substituents.
The P-Al-P angles of dialkyls 2a, 2b, 2c, 3b, and 3c
are slightly sharper than those of dichloride 5b and
dihydride 6b. The discrepancy in P-Al-P angles of
dialkyls versus dichloride or dihydride is somewhat in
accord with the observed 2JPP coupling constants found
(35) Schrock, R. R.; Seidel, S. W.; MoschZanetti, N. C.; Shih, K. Y.; MB,
O. D.; Davis, W. M.; Reiff, W. M. J. Am. Chem. Soc. 1997, 119, 11876–
11893.
(36) Schrock, R. R.; Seidel, S. W.; MoschZanetti, N. C.; Dobbs, D. A.;
Shih, K. Y.; Davis, W. M. Organometallics 1997, 16, 5195–5208.
(37) Schrock, R. R.; Cummins, C. C.; Wilhelm, T.; Lin, S.; Reid, S. M.;
Kol, M.; Davis, W. M. Organometallics 1996, 15, 1470–1476.
(38) Waugh, J. S.; Cotton, F. A. J. Phys. Chem. 1961, 65, 562–563.
(39) Akitt, J. W. Prog. NMR Spectrosc. 1989, 21, 1.
(40) Delpuech, J. J. NMR of Newly Accessible Nuclei; Academic Press:
New York, 1983; Vol 2.
(41) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; p 93.

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5483
Table 1. Crystallographic Data for 2a, 2b, 2c, 3b, 3c, 5b, and 6b
[Ph-PNP]AlMe2 (2a)
[iPr-PNP]AlMe2 (2b)
[Ph-PNP-Pr]AlMe2 (2c)
formula
fw
C
38H34AlNP2
C33H50AlNP2
549.66
monoclinic
P21/a
15.0610(3)
14.6720(3)
15.6740(3)
90
108.1360(10)
90
3291.49(11)
4
1.109
50.06
22662
C32H38AlNP2
525.55
triclinic
593.58
monoclinic
C2/c
19.5904(10)
9.7111(5)
18.8411(11)
90
cryst syst
space group
P1
˚
a (A)
9.4805(3)
11.5257(3)
16.6500(6)
108.584(2)
96.379(2)
107.357(2)
1602.63(9)
2
1.089
55.28
22264
5780
0.182
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
112.537(2)
90
3310.7(3)
4
1.191
50.68
10273
3008
0.184
˚
V (A3)
Z
Dcalcd (Mg/m3)
2θmax(deg)
total reflns
independent reflns
5796
0.180
abs coeff (mm -1
)
data/restraints/ params
no. observed data
Rint
3008/ 0/192
1795
0.0983
5796/ 0/343
4145
0.0753
5780/0/325
3398
0.1074
goodness of fit
final R indices
[I > 2σ(I)]
0.977
1.051
0.847
R1 = 0.0957
wR2 = 0.2214
R1 = 0.1591
wR2 = 0.2943
R1 = 0.0582
wR2 = 0.1148
R1 = 0.0883
wR2 = 0.1629
R1 = 0.0767
wR2 = 0.2232
R1 = 0.1316
wR2 = 0.2612
R indices (all data)
[Pr-PNP]AlEt2 (3b)
[Ph-PNP-Pr]AlEt2 (3c)
[Pr-PNP]AlCl2 (5b)
[iPr-PNP]AlH2 (6b)
formula
fw
C28H46AlNP2
485.58
triclinic
C34H42AlNP2
553.61
monoclinic
P21/n
9.7634(2)
14.2656(4)
22.6357(6)
90
91.8880(10)
90
3151.01(14)
4
1.167
50.70
18635
C24H36AlCl2NP2
498.36
C24H38AlNP2
429.47
orthorhombic
Pcab
11.6641(3)
29.3264(7)
29.9414(9) 90
90
cryst syst
space group
monoclinic
P2/a
17.2082(4)
9.2626(3)
18.4636(6)
90
116.8740(10)
90
2625.13(14)
4
1.261
P1
˚
a (A)
9.19800(10)
18.7320(2)
19.0670(3)
62.1130(10)
86.9810(10)
87.6650(10)
2899.17(6)
4
1.112
50.14
40129
10229
0.196
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
90
90
˚
V (A3)
10241.9(5)
16
1.114
50.70
31956
Z
Dcalcd (Mg/m3)
2θmax (deg)
total reflns
independent reflns
50.64
16573
4770
0.415
5659
0.189
9158
0.214
abs coeff (mm -1
)
data/restraints/ params
no. observed data
Rint
10229/ 0/577
8070
0.0694
5659/0/344
4212
0.0765
4770/ 0/274
3684
0.0816
9158/0/505
4596
0.1447
goodness of fit
final R indices
[I > 2σ(I)]
1.061
1.107
1.224
1.099
R1 = 0.0469
wR2 = 0.1116
R1 = 0.0655
wR2 = 0.1217
R1 = 0.0621
wR2 = 0.1495
R1 = 0.0933
wR2 = 0.1764
R1 = 0.1111
wR2 = 0.3116
R1 = 0.1398
wR2 = 0.3355
R1 = 0.0957
wR2 = 0.2138
R1 = 0.2040
wR2 = 0.2761
R indices (all data)
for the [Ph-PNP-iPr]--derived dialkyls 2c-4c versus
dichloride 5c or dihydride 6c (vide supra). In comparison,
the P-M-P angles for four-coordinate group 10
complexes of these amido diphosphine ligands are
much wider, for example, [iPr-PNP]NiH (175.05(4)°),25
[Ph- PNP]NiMe (169.05(9)°),19 [iPr-PNP]NiMe (166.68
(5)°),19 [Ph-PNP-iPr]Ni(n-hexyl) (165.65(9)°),25 [Ph-PNP]
PdCl (165.27(11)°),22 and [Ph-PNP]PtCl (167.30(8)°).20
The sharper P-M-P angles for M = Al versus those
of M = group 10 metals are ascribed to longer
M-P bonds for the former, given that the M-N and
M-X (X = C, Cl) distances are very similar. This leads to
a closer contact for the two CH moieties ortho to the
amido nitrogen in the C2v form of the aluminum
species and thus a larger dihedral angle between two
N-phenylene-P mean planes in the solid state. As a result,
the flipping exchange barrier is much higher. Table S2
(Supporting Information) summarizes the dihedral
angles of representative examples for comparison. To
illustrate, two views of the X-ray structures of 2b (left)
and [iPr-PNP]NiMe (right) are depicted in Figure S5
(Supporting Information), highlighting the spatial orien-
tation of the two aromatic CH groups ortho to the amido
nitrogen donor (top) and the “wedge” formed by the two
o-phenylene rings in the ligand backbone (bottom). No-
tably, the “wedge” in [iPr-PNP]NiMe is much sharper. In
2b, both CH11 and CH14 moieties are oriented such that
the transient C2v structure proposed in Scheme 2 is rather
inaccessible. The corresponding space available for the
nickel species to undergo such exchange, however, is
much larger. Consistent with the relatively short Al-P
distances and acute dihedral angles found for 5b, the

5484 Inorganic Chemistry, Vol. 48, No. 12, 2009
Lee and Liang
a
˚
Table 2. Selected Bond Distances (A) for 2a, 2b, 2c, 3b, 3c, 5b, and 6b
compound
Al-N
Al-Xa
Al-P
[Ph-PNP]AlMe2 (2a)
[iPr-PNP]AlMe2 (2b)
[Ph-PNP-iPr]AlMe2 (2c)
[iPr-PNP]AlEt2 (3b)b
[iPr-PNP]AlEt2 (3b)c
[Ph-PNP-iPr]AlEt2 (3c)
[iPr-PNP]AlCl2 (5b)b
[iPr-PNP]AlCl2 (5b)c
[iPr-PNP]AlH2 (6b)b
[iPr-PNP]AlH2 (6b)c
1.940(7)
1.935(2)
2.019(4)
1.9287(19)
1.9400(19)
1.915(3)
1.932(10)
1.916(10)
1.899(6)
1.913(6)
1.968(6), 1.968(6)
1.969(3), 1.977(3)
1.823(6), 2.045(5)
1.977(3), 1.986(3)
1.983(2), 1.985(2)
1.978(3), 1.984(3)
2.198(3), 2.198(3)
2.201(3), 2.201(3)
1.3279, 1.3602
2.6202(13), 2.6202(13)
2.6343(10), 2.6246(10)
2.5499(18), 2.7902(17)
2.6514(9), 2.6578(9)
2.6300(9), 2.6234(9)
2.5700(13), 2.8038(13)
2.481(2), 2.481(2)
2.497(2), 2.497(2)
2.570(2), 2.590(2)
2.543(2), 2.545(3)
1.3747, 1.3677
a X represents an R-carbon, a chloride, or a hydrogen atom. b The data summarized represent one of the two independent molecules found in the
asymmetric unit cell. c The data summarized represent one of the two independent molecules found in the asymmetric unit cell.
Table 3. Selected Bond Angles (deg) for 2a, 2b, 2c, 3b, 3c, 5b, and 6ba
compound
N-Al-P
P-Al-P
P-Al-X a
N-Al-X a
X-Al-X a
[Ph-PNP]AlMe2 (2a)
77.64(6),
77.64(6)
155.28(12)
96.12(18),
96.12(18),
96.36(18),
96.36(18)
96.73(10),
95.72(10),
96.35(10),
96.20(10)
101.89(17),
100.13(15),
87.53(17),
96.71(14)
93.68(8),
99.08(8),
99.59(8),
93.58(8)
93.74(8),
99.27(7),
99.60(7),
92.77(7)
104.72(11),
98.28(11),
88.12(11),
92.46(11)
97.12(8),
93.93(8),
93.93(8),
97.12(8)
120.5(2),
120.5(2)
119.0(5)
[iPr-PNP]AlMe2 (2b)
[Ph-PNP-iPr]AlMe2 (2c)
[iPr-PNP]AlEt2 (3b)b
[iPr-PNP]AlEt2 (3b)c
[Ph-PNP-iPr]AlEt2 (3c)
[iPr-PNP]AlCl2 (5b)b
[iPr-PNP]AlCl2 (5b)c
77.65(7),
77.31(7)
154.95(4)
152.52(7)
155.62(3)
156.23(3)
154.40(5)
160.36(18)
159.72(18)
120.16(14),
120.14(13)
119.70(16)
121.1(3)
79.20(11),
73.36(11)
112.7(2),
124.8(2),
77.84(6),
77.79(6)
122.10(10),
122.50(10)
115.40(12)
115.18(11)
123.66(16)
111.32(19)
114.0(2)
77.97(6),
78.27(6)
122.24(10),
122.58(10)
80.21(8),
74.21(8)
117.70(14),
116.50(14)
80.18(9),
80.18(9)
124.34(10),
124.34(10)
79.86(9),
79.86(9)
96.95(8),
94.05(8),
94.05(8),
96.95(8)
93.2,95.7,
87.6, 104.5
97.3, 86.8,
98.1, 91.4
123.00(11),
123.00(11)
[iPr-PNP]AlH2 (6b)b
[iPr-PNP]AlH2 (6b)c
79.72(16),
79.31(16)
79.41(16),
80.32(16)
159.11(11)
159.60(11)
112.7, 127.4
118.8
139.4
104.5,
115.1,
a X represents an R-carbon, a chloride, or a hydrogen atom. b The data summarized represent one of the two independent molecules found in the
asymmetric unit cell. c The data summarized represent one of the two independent molecules found in the asymmetric unit cell.
flipping exchange barrier of this molecule is the lowest
among the aluminum species investigated. A variable-
temperature 1H NMR study revealed that the isopropyl-
methine resonances of 5b (60 mM in toluene-d8) coalesce
at 80 °C.
Catalytic Polymerization. Preliminary studies revealed
that organoaluminum complexes of these amido dipho-
sphine ligands are highly42 active initiators for catalytic
R-olefin polymerization. In the presence of B(C6F5)3,
2a-c reacts with ethylene or 1-hexene at room tempera-
ture catalytically to produce the corresponding poly-
mers with activities of ca. 4 ꢀ 105 g molcat -1 h-1 atm-1 or
3 ꢀ 104 g molcat -1 h-1, respectively.
Conclusions
We have prepared and characterized a series of organoa-
luminum complexes of diarylamido diphosphine ligands.
Solution NMR and X-ray crystallographic studies reveal a
five-coordinate nature for these species in which the triden-
tate amido diphosphine ligands adopt a meridional coordi-
nation mode. With the incorporation of the relatively rigid
o-phenylene in the ligand backbone, phosphine dissociation
from the aluminum center of these molecules was not
observed, even in the presence of coordinating solvents such
(42) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed.
1999, 38, 429–447.

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5485
as THF or Et2O. The solution symmetry of these aluminum
complexes is notably lower than that of the corresponding
four-coordinate group 10 derivatives. NMR studies indicate
that the symmetrically substituted [Ph-PNP]- and [iPr-
PNP]- complexes are C2-symmetric, while [Ph-PNP-iPr]-
derivatives are C1. The R-hydrogen atoms in these dialkyl
complexes are diastereotopic. Depending on steric demand of
the substituents at phosphorus and R-carbon atoms, well-
resolved multiplet resonances may be observed by 1H NMR
spectroscopy. Interestingly, the 2JPP coupling constants ob-
served in [Ph-PNP-iPr]- complexes appear to correlate well
with the P-M-P angles (M = Al or group 10 metals)
established by X-ray crystallography. In the presence of B
(C6F5)3, these aluminum complexes are active initiators for
catalytic R-olefin polymerization.
Synthesis of [iPr-PNP]AlMe2 (2b). Colorless crystals
suitable for X-ray diffraction analysis were grown by layering
pentane on a concentrated diethyl ether solution at -35 °C.
Yield: 81%. 1H NMR (C6D6, 500 MHz): δ 7.28 (m, 2, Ar), 7.02
(m, 4, Ar), 6.72 (t, 2, J = 7, Ar), 2.07 (m, 2, CHMe2), 1.79 (m, 2,
CHMe2), 1.12 (dd, 6, CHMe2), 1.07 (dd, 6, CHMe2), 1.04 (dd, 6,
CHMe2), 0.85 (dd, 6, CHMe2), -0.10 (t, 6, 3JHP = 5.5, AlMe2).
31P{1H} NMR (C6D6, 202.31 MHz): δ -17.66. 13C{1H} NMR
(C6D6, 125.5 MHz): δ 160.89 (t, JCP = 11.04, C), 133.19 (s, CH),
131.41 (s, CH), 121.43 (t, JCP = 1.76, CH), 119.34 (s, CH),
119.22 (d, JCP = 6.40, C), 23.31 (br s, CHMe2), 19.80
(t, JCP = 4.14, CHMe2), 19.70 (t, JCP = 3.14, CHMe2), 19.63
(m, CHMe2), 19.26 (t, JCP = 7.41, CHMe2), 16.91 (br s,
2
CHMe2), -1.83 (t, JCP = 34.45, AlMe2). Anal. calcd for
C26H42AlNP2: C, 68.23; H, 9.26; N, 3.06. Found: C, 67.86; H,
9.25; N, 3.04.
Synthesis of [Ph-PNP-iPr]AlMe2 (2c). Colorless crystals
suitable for X-ray diffraction analysis were grown by layering
diethyl ether on a concentrated toluene solution at -35 °C.
Yield: 78%. 1H NMR (C6D6, 500 MHz): δ 7.55 (m, 4, Ar), 7.44
(dt, 1, J = 1.5 and 7.5, Ar), 7.22 (dd, 1, J = 5.5 and 7.5, Ar), 7.13
(m, 1, Ar), 7.05 (m, 6, Ar), 6.99 (m, 1, Ar), 6.90 (m, 2, Ar), 6.69 (t,
1, J = 7.5, Ar), 6.61 (t, 1, J = 7, Ar), 2.01 (m, 1, CHMe2), 1.77
(m, 1, CHMe2), 1.01 (dd, 3, CHMe2), 1.03 (dd, 3, CHMe2), 1.00
(dd, 3, CHMe2), 0.84 (dd, 3, CHMe2), 0.09 (dd, 3, 3JHP = 5 and
Experimental Section
General Procedures. Unless otherwise specified, all experi-
ments were performed under nitrogen using standard Schlenk or
glovebox techniques. All solvents were reagent-grade or better
and purified by standard methods. All other chemicals were
obtained from commercial vendors and used as received. The
NMR spectra were recorded on Varian instruments. Chemical
shifts (δ) are listed as parts per million downfield from tetra-
methylsilane, and coupling constants (J) and peak widths at
3
5.5, AlMe), -0.06 (dd, 3, JHP = 5 and 5.5, AlMe). 31P{1H}
NMR (C6D6, 202.31 MHz): δ -15.63 (d, 1, 2JPP = 8.70, PiPr2),
-20.89 (d, 1, 2JPP = 8.70, PPh2). 13C{1H} NMR (C6D6, 125.5
MHz): δ 161.71 (dd, JCP = 1.38 and 18.83, C), 158.86 (dd, JCP
= 1.88 and 22.46, C), 135.50 (d, JCP = 3.26, C), 134.79 (s, CH),
134.62 (d, JCP = 3.64, C), 134.43 (d, JCP = 15.19, CH), 134.22
(d, JCP = 15.56, CH), 132.89 (s, CH), 132.21 (s, CH), 131.73
(s, CH), 129.71 (s, CH), 129.37 (s, CH), 129.19 (d, JCP = 7.28,
CH), 129.06 (d, JCP = 7.28, CH), 126.71 (d, JCP = 16.44, C),
121.90 (s, CH), 121.87 (s, CH), 121.14 (d, JCP = 2.26, CH),
119.31 (d, JCP = 3.77, CH), 117.39 (d, JCP = 25.60, C), 23.05 (d,
JCP = 6.90, CHMe2), 19.97 (d, JCP = 12.30, CHMe2), 19.56
(d, JCP = 5.90, CHMe2), 19.43 (d, JCP = 5.02, CHMe2), 19.16
(d, JCP = 11.92, CHMe2), 17.16 (d, JCP = 3.64, CHMe2), -3.28
(dd, 2JCP = 32.88 and 33.01, AlMe), -5.17 (dd, 2JCP = 28.74
and 29.74, AlMe). Anal. calcd for C32H38AlNP2: C, 73.13; H,
7.29; N, 2.67. Found: C, 73.58; H, 7.34; N, 2.42.
1
half-height (Δν1/2) are in hertz. H and 13C NMR spectra are
referenced to an internal solvent peak at δ 7.16 and δ 128.39,
respectively, for C6D6. The assignment of the carbon atoms for
all new compounds is based on the DEPT 13C NMR spectro-
scopy. 31P NMR spectra are referenced externally using 85%
H3PO4 at δ 0. Routine coupling constants are not listed.
Elemental analysis was performed on a Heraeus CHN-O Rapid
analyzer. With multiple attempts, we were not able to obtain
satisfactory analysis for some complexes reported herein due to
extreme moisture-sensitivity of these derivatives.
X-Ray Crystallography. Table 1 summarizes the crystal-
lographic data for all structurally characterized compounds.
Data were collected at 200 K on a Bruker-Nonius Kappa CCD
diffractometer with graphite monochromated Mo KR radiation
˚
(λ = 0.7107 A). Structures were solved by direct methods and
refined by full-matrix least-squares procedures against F2 using
maXus or WinGX crystallographic software package. All full-
weight nonhydrogen atoms were refined anisotropically. Hy-
drogen atoms were placed in calculated positions. The crystals
of [iPr-PNP]AlCl2 (5b) were of poor quality but sufficient to
establish the identity of this molecule.
1
Synthesis of [Ph-PNP]AlEt2 (3a). Yield: 81%. H NMR
(C6D6, 500 MHz): δ 7.56 (m, 8, Ar), 7.03 (m, 16, Ar), 6.94 (td, 2,
Ar), 6.59 (t, 2, J = 7.5, Ar), 1.31 (t, 6, J = 8.5, AlCH2Me), 0.80
(m, 4, AlCH2Me). 31P{1H} NMR (C6D6, 202.31 MHz):
δ -20.53. 13C{1H} NMR (C6D6, 125.5 MHz): δ 160.38 (m,
C), 134.39 (m, CH), 133.95 (m, CH), 133.86 (m, CH), 133.55 (m,
C), 133.44 (m, C), 132.48 (s, CH), 130.19 (s, CH), 129.87 (s, CH),
129.31 (m, CH), 129.26 (m, CH), 124.04 (dd, JCP = 28.80 and
1.76, C), 121.74 (s, CH), 121.09 (s, CH), 10.82 (t, 3JCP = 2.76,
General Procedures for Synthesis of 2a-c, 3a-c, and
4a-c. To a toluene solution of 1a, 1b, or 1c at -35 °C was added
AlR3 (1 equiv, R = Me, Et, Bu). The reaction solution was
i
2
naturally warmed to room temperature with stirring. After
being stirred at room temperature overnight, the reaction solu-
tion was filtered through a pad of Celite, concentrated under
reduced pressure, and cooled to -35 °C to afford the product as
a pale yellow or colorless solid.
AlCH2Me), 3.49 (t, JCP = 28.87, AlCH2Me). Anal. calcd for
C40H38AlNP2: C, 77.27; H, 6.17; N, 2.25. Found: C, 77.43; H,
6.55; N, 2.55.
Synthesis of [iPr-PNP]AlEt2 (3b). Colorless crystals sui-
table for X-ray diffraction analysis were grown by layering
pentane on a concentrated diethyl ether solution at -35 °C.
Yield: 87%. 1H NMR (C6D6, 500 MHz): δ 7.23 (dd, 2, J = 4 and
8, Ar), 7.02 (m, 4, Ar), 6.72 (t, 2, J = 7.5, Ar), 2.13 (m, 2,
CHMe2), 1.84 (m, 2, CHMe2), 1.47 (t, 6, J = 8, AlCH2CH3),
1.14 (dd, 6, CHMe2), 1.10 (dd, 6, CHMe2), 1.04 (dd, 6, CHMe2),
0.84 (dd, 6, CHMe2), 0.43 (m, 2, AlCHAHB), 0.36 (m, 2,
AlCHAHB). 31P{1H} NMR (C6D6, 202.31 MHz): δ -16.76.
13C{1H} NMR (C6D6, 125.5 MHz): δ 161.00 (m, JCP = 10.542,
C), 133.16 (s, CH), 131.31 (s, CH), 121.56 (t, JCP = 2.26, CH),
119.38 (s, CH), 118.89 (m, C), 23.71 (s, CHMe2), 19.79 (m,
CHMe2), 19.52 (t, JCP = 4.14, CHMe2), 19.26 (t, 3JCP = 6.90,
CHMe2), 16.58 (t, 3JCP = 2.76, CHMe2), 12.12 (t, 3JCP = 5.40,
AlCH2CH3), 5.39 (t, 2JCP = 32.00, AlCH2CH3). Anal. calcd for
Synthesis of [Ph-PNP]AlMe2 (2a). Colorless crystals sui-
table for X-ray diffraction analysis were grown by layering THF
on a concentrated toluene solution at -35 °C. Yield: 83%.
1H NMR (C6D6, 500 MHz): δ 7.56 (t, 4, J = 7.5, Ar), 7.48 (t, 4,
J = 7.5, Ar), 7.01 (m, 16, Ar), 6.92 (t, 2, J = 7.75, Ar), 6.59 (t, 2,
J = 7.5, Ar), 0.14 (t, 6, 3JHP = 6, AlMe2). 31P{1H} NMR (C6D6,
202.31 MHz): δ -19.66. 13C{1H} NMR (C6D6, 125.5 MHz): δ
159.89 (m, C), 134.32 (m, CH), 134.16 (m, CH), 134.05 (s, CH),
133.32 (m, C), 132.80 (m, C), 132.48 (s, CH), 130.30 (s, CH),
129.75 (s, CH), 129.28 (m, CH), 129.21 (m, CH), 124.32 (m, C),
121.72 (s, CH), 121.02 (s, CH), -5.94 (t, 2JCP = 32.13, AlMe2).
Anal. calcd for (C38H34AlNP2)(THF)2: C, 74.87; H, 6.84; N,
1.90. Found: C, 74.78; H, 6.87; N, 2.37.

5486 Inorganic Chemistry, Vol. 48, No. 12, 2009
Lee and Liang
125.5 MHz): δ 161.68 (d, JCP = 18.32, C), 158.60 (dd, JCP
1.88 and 23.85, C), 136.57 (s, C), 135.94 (s, C), 135.18 (s, CH),
134.57 (d, JCP = 15.56, CH), 133.94 (d, JCP = 15.56, CH),
132.73 (s, CH), 132.15 (s, CH), 131.66(s, CH), 129.43 (s, CH),
129.31 (s, CH), 129.08 (d, JCP = 6.40, CH), 129.48 (d, JCP =
7.41, CH), 127.61 (d, JCP = 11.92, C), 123.13 (d, JCP = 3.64,
CH), 121.65 (s, CH), 121.60 (d, JCP = 4.64, CH), 119.01 (d,
C28H46AlNP2: C, 69.24; H, 9.55; N, 2.89. Found: C, 69.60; H,
9.21; N, 2.59.
=
Synthesis of [Ph-PNP-iPr]AlEt2 (3c). Colorless crystals
suitable for X-ray diffraction analysis were grown by layering
diethyl ether on a concentrated toluene solution at -35 °C.
Yield: 88%. 1H NMR (C6D6, 500 MHz): δ 7.59 (dt, 2, Ar), 7.54
(dt, 2, Ar), 7.21 (m, 1, Ar), 7.13 (m, 1, Ar), 7.05 (m, 7, Ar), 6.99
(m, 1, Ar), 6.91 (m, 2, Ar), 6.68 (t, 1, J = 7, Ar), 6.62 (t, 1, J = 7,
Ar), 2.07 (m, 1, CHMe2), 1.85 (m, 1, CHMe2), 1.47 (t, 3, J = 8,
AlCH2CH3), 1.26 (t, 3, J = 8, AlCH2CH3), 1.09 (dd, 3, CHMe2),
1.06 (dd, 3, CHMe2), 1.04 (dd, 3, CHMe2), 0.84 (dd, 3, CHMe2),
0.79 (m, 1, AlCHAHB), 0.57 (m, 2, AlCH2), 0.50 (m, 1,
AlCHAHB). 31P{1H} NMR (C6D6, 202.31 MHz): δ -14.92 (d,
JCP = 3.64, CH), 116.52 (d, JCP = 24.72, C), 29.82 (s, CHMe2),
29.33 (s, CHMe2), 28.71 (s, CHMe2), 28.64 (s, CHMe2), 28.21
(m, CHMe2), 28.11 (m, CHMe2), 26.13 (m, AlCH2CHMe2),
25.94 (m, AlCH2CHMe2), 23.13 (d, JCP = 7.28, CHMe2), 20.78
(d, JCP = 10.92, CHMe2), 19.75 (d, JCP = 6.40, CHMe2), 19.57
(d, JCP = 4.52, CHMe2), 19.04 (d, JCP = 10.04, CHMe2), 17.08
(d, JCP = 3.64, CHMe2). Anal. calcd for C38H50AlNP2:
C, 74.84; H, 8.27; N, 2.30. Found: C, 74.78; H, 7.92; N, 2.35.
Synthesis of [iPr-PNP]AlCl2 (5b). Method 1. To a pre-
chilled toluene (3 mL) solution of [iPr-PNP]Li(OEt2) (230 mg,
0.48 mmol) at -35 °C was added solid trichloroaluminum
(64 mg, 0.48 mmol). The reaction solution was naturally
warmed to room temperature with stirring. After being stirred
at room temperature for 26 h, the reaction solution was filtered
through a pad of Celite, which was further washed with toluene
(ca. 2 mL). The combined filtrate was concentrated under
reduced pressure and cooled to -35 °C to afford the product
as a pale-yellow solid. Yield: 180 mg (76%). Colorless crystals
suitable for X-ray diffraction analysis were grown from a
concentrated toluene solution at -35 °C.
2
2JPP = 9.10, PiPr2), -20.38 (d, JPP = 9.10, PPh2). 13C{1H}
NMR (C6D6, 125.5 MHz): δ 161.89 (d, JCP = 18.20, C), 159.25
(dd, JCP = 1.76 and 22.84, C), 135.65 (d, JCP = 3.26, C), 135.26
(d, JCP = 3.26, C), 134.78 (s, CH), 134.48 (d, JCP = 15.19, CH),
133.89 (d, JCP = 15.56, CH), 132.74 (s, CH), 132.15 (s, CH),
131.73 (s, CH),129.66 (s, CH), 129.39 (s, CH), 129.17 (d, JCP
=
6.78, CH), 129.09 (d, JCP = 7.28, CH), 126.10 (d, C), 121.89 (s,
CH), 121.85 (s, CH), 121.12 (d, JCP = 2.64, CH), 119.37 (d, JCP
= 3.64, CH), 117.24 (d, JCP = 24.72, C), 23.24 (d, JCP = 5.52,
CHMe2), 20.08 (d, JCP = 11.42, CHMe2), 19.68 (d, JCP = 6.40,
CHMe2), 19.18 (d, JCP = 8.66, CHMe2), 19.12 (d, JCP = 2.39,
CHMe2), 16.85 (d, JCP = 4.52, CHMe2), 11.54 (dd, 3JCP = 3.64
and 5.52, AlCH2CH3), 10.96 (t, 3JCP = 2.26, AlCH2CH3), 4.75
2
2
(dd, JCP = 24.72 and 30.25, AlCH2CH3), 3.64 (dd, JCP
=
26.98 and 27.36, AlCH2CH3). Anal. calcd for C34H42AlNP2: C,
73.74; H, 7.65; N, 2 0.53. Found: C, 73.70; H, 7.12; N, 2.48.
Synthesis of [Ph-PNP]AliBu2 (4a). Yield: 78%. 1H NMR
(C6D6, 500 MHz): δ 7.65 (dt, 4, Ar), 7.51 (dt, 4, Ar), 7.13 (m, 4,
Ar), 7.06 (m, Ar), 6.99 (m, Ar), 6.61 (t, 2, J = 7.5, Ar), 2.13 (m, 2,
AlCH2CHMe2), 1.12 (d, 6, AlCH2CHMe2), 0.99 (d, 6,
AlCH2CHMe2), 0.74 (m, 4, AlCH2CHMe2). 31P{1H} NMR
(C6D6, 202.31 MHz): δ -20.12. 13C{1H} NMR (C6D6, 125.5
MHz): δ 160.38 (m, C), 135.23 (m, CH), 134.63 (d, JCP = 11.42,
C), 134.38 (s, CH), 133.95 (m, CH), 133.54 (d, JCP = 12.80, C),
Method 2. To a prechilled toluene solution (0.6 mL) of 1b
(8 mg, 0.02 mmol) at -35 °C was added MeAlCl2 (0.02 mL, 1 M
in hexane, 0.02 mmol). The solution was transferred to a Teflon-
sealed NMR tube and examined by 31P{1H} NMR spectro-
scopy, which showed quantitative formation of 5b in 15 min.
1H NMR (C6D6, 500 MHz): δ 7.29 (dd, 2, J = 4.5 and 8, Ar),
7.02 (t, 2, J = 7.75, Ar), 6.92 (t, 2, J = 6.25, Ar), 6.68 (t, 2, J = 7,
Ar), 2.14 (m, 2, CHMe2), 2.11 (m, 2, CHMe2), 1.31 (dd, 6, J = 7
and 15, CHMe2), 1.26 (dd, 6, J = 7 and 17, CHMe2), 1.12 (dd, 6,
J = 7 and 15.5, CHMe2), 0.79 (dd, 6, J = 7 and 10.5, CHMe2).
31P{1H} NMR (C6D6, 202.31 MHz): δ 20.10. 13C{1H} NMR
(C6D6, 125.5 MHz): δ 157.94 (dd, JCP = 4.14 and 15.12, C),
133.45 (s, CH), 132.24 (s, CH), 120.14 (t, JCP = 2.39, CH),
119.41 (t, JCP = 2.76, CH), 115.87 (d, JCP = 31.50, C), 22.71 (d,
JCP = 13.68, CHMe2), 19.42 (d, JCP = 18.20, CHMe2), 19.06
132.58 (s, CH), 130.30 (s, CH), 130.11 (s, CH), 129.47 (t, JCP
=
3.64, CH), 129.30 (t, JCP = 3.36, CH), 124.16 (dd, JCP = 1.76
and 5.48, C), 122.38 (t, JCP = 1.88, CH), 121.41 (s, CH), 29.73 (s,
AlCH2CHMe2), 28.47 (s, AlCH2CHMe2), 28.05 (t, 3JCP = 2.76,
AlCH2CHMe2), 25.32 (t, 2JCP = 26.10, AlCH2CHMe2). Anal.
calcd for C44H46AlNP2: C, 77.96; H, 6.85; N, 2.07. Found: C,
77.92; H, 6.36 ; N, 2.54.
Synthesis of [iPr-PNP]AliBu2 (4b). Yield: 89%. 1H NMR
(C6D6, 500 MHz): δ 7.23 (dd, 2, J = 3.5 and 8, Ar), 7.02 (m, 4,
Ar), 6.72 (t, 2, J = 4.75, Ar), 2.16 (m, 2, C HMe2), 2.04 (m, 2,
AlCH2CHMe2), 1.85 (m, 2, CHMe2), 1.33 (d, 6, J = 6.5,
AlCH2CHMe2), 1.24 (d, 6, AlCH2CHMe2), 1.18 (dd, 6,
CHMe2), 1.14 (dd, 6, CHMe2), 1.04 (dd, 6, CHMe2), 0.84 (dd,
6, CHMe2), 0.44 (dd, 2, J = 4 and 13.5, AlCHAHB), 0.29 (m, 2,
(br s, CHMe2), 18.21 (d, JCP = 10.17, CHMe2), 16.48 (d, JCP =
6.90, CHMe2). Anal. calcd for C24H36AlCl2NP2: C, 57.82; H,
7.28; N, 2.81. Found: C, 57.24; H, 7.40; N, 2.73.
General Procedures for Synthesis of 6a-c. To a THF
solution of 1a, 1b, or 1c at -35 °C was added n-BuLi (1 equiv).
The reaction solution was stirred at room temperature for 1 h
and cooled to -35 °C again. Solid AlCl3 (1 equiv) was added.
The reaction mixture was stirred at room temperature for 1 h.
The 31P{1H} NMR spectra (THF, 80.95 MHz) of a reaction
aliquot at this moment revealed the presence of the presumed 5a
AlCHAHB). 31P{1H} NMR (C6D6, 202.31 MHz): δ -17.56. 13
C
at -29.43 ppm, 5b at -21.01 ppm, or 5c at -18.11 (d, 1, 2JPP
=
{1H} NMR (C6D6, 125.5 MHz): δ 160.56 (m, C), 133.08 (s, CH),
131.23 (s, CH), 121.87 (t, JCP = 2.26, CH), 119.42 (s, CH),
118.93 (m, C), 30.29 (s, CHMe2), 28.73 (t, JCP = 6.90, CHMe2),
28.47 (m, AlCH2CHMe2), 28.36 (s, CHMe2), 24.00 (s, CHMe2),
20.04 (m, CHMe2), 19.88 (t, JCP = 4.14, CHMe2), 19.85 (t, JCP
47.64, PiPr2) and -30.84 (d, 1, 2JPP = 47.64, PPh2) ppm. Solid
LiAlH4 (1 equiv) was then added at room temperature. The
reaction mixture was stirred at room temperature for 1 h. All
volatiles were removed in vacuo. The product was extracted
with toluene followed by filtration with Celite. Evaporation of
toluene under reduced pressure gave an off-white solid.
= 3.14, CHMe2), 18.96 (t, JCP = 6.90, CHMe2), 16.31 (t, JCP
2.76, CHMe2). Anal. calcd for C32H54AlNP2: C, 70.95; H, 10.05;
=
N, 2.59. Found: C, 71.56; H, 10.45; N, 2.65.
Synthesis of [Ph-PNP]AlH2 (6a). Yield: 76%. The
dichloride 5a could be alternatively prepared in situ by the
addition of 1 equiv of MeAlCl2 to 1a in toluene at -35 °C.
11H NMR (C6D6, 500 MHz): δ 7.70 (m, 4, Ar), 7.57 (m, 4, Ar),
7.17 (m, 4, Ar), 7.04 (m, 4, Ar), 6.99 (m, 8, Ar), 6.88 (td, 2, Ar),
6.57 (t, 4, Ar), 5.51 (br s, 2, Δν1/2 = 132, AlH). 31P{1H} NMR
(C6D6, 202.31 MHz): δ -27.35 (Δν1/2 = 4.7). 13C{1H} NMR
(C6D6, 125.5 MHz): δ 159.27 (t, JCP = 10.92, C), 134.63 (s, CH),
134.53 (d, JCP = 7.28, CH), 134.15 (t, JCP = 6.40, CH), 132.48
(s, CH), 132.25 (dd, JCP = 10.54 and 12.30, C), 130.95 (dd,
Synthesis of [Ph-PNP-iPr]AliBu2 (4c). Yield: 88%. 11H
NMR (C6D6, 500 MHz): δ 7.65 (t, 2, J = 7.5, Ar), 7.50 (t, 2, J =
8, Ar), 7.22 (m, 2, Ar), 7.12 (m, 2, Ar), 7.04 (m, 6, Ar), 6.92 (m, 2,
Ar), 6.70 (t, 1, J = 7.5, Ar), 6.62 (t, 1, J = 7.5, Ar), 2.15 (m, 3,
CHMe2), 1.90 (m, 1, CHMe2), 1.24 (m, 6, CHMe2), 1.10 (m, 15,
CHMe2), 0.85 (m, 3, CHMe2), 0.69 (m, 1, AlCHAHB), 0.64 (m, 1,
0
0
0
0
AlCHAHB), 0.50 (m, 1, AlCHA HB ), 0.42 (m, 1, AlCHA HB ).
31P{1H} NMR (C6D6, 202.31 MHz): δ -14.86 (d, 1, 2JPP = 9.10,
PiPr2), -18.90 (d, 1, 2JPP = 9.10, PPh2). 13C{1H} NMR (C6D6,

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5487
JCP = 10.54 and 9.16, C), 130.67 (s, CH), 130.03 (s, CH), 129.42
(t, JCP = 4.52, CH), 129.19 (t, JCP = 4.52, CH), 122.25 (dd,
CH), 129.15 (d, JCP = 14.68, CH), 128.68 (s, CH), 123.08 (d,
JCP = 27.48, C), 121.24 (d, JCP = 4.52, CH), 120.67 (d, JCP =
J
CP = 17.44 and 15.56, C), 120.97 (t, JCP = 1.88, CH), 120.34
3.64, CH), 119.85 (d, JCP = 3.64, CH), 119.43 (d, JCP = 4.52,
CH), 116.84 (d, JCP = 25.60, C), 22.91 (d, JCP = 7.28, CHMe2),
19.97 (d, JCP = 13.81, CHMe2), 19.51 (d, JCP = 4.52, CHMe2),
19.19 (d, JCP = 11.04, CHMe2), 19.00 (d, JCP = 5.52, CHMe2),
16.67 (d, JCP = 5.40, CHMe2). Anal. calcd for C30H34AlNP2:
C, 72.41; H, 6.89; N, 2.82. Found: C, 72.90; H, 6.33; N, 2.99.
Catalytic Ethylene Polymerization. A chlorobenzene so-
lution (0.25 mL) of B(C6F5)3 (2.5 μmol) was added to a toluene
solution (5 mL) of 2 (2.625 μmol) at room temperature. To this
solution was introduced ethylene (1 atm) at room temperature
for 2 min with stirring. The reaction was quenched with MeOH
(ca. 1 mL). All volatiles were removed under reduced pressure
(ca. 100 mTorr at 70 °C) until the product weight remained
constant.
(t, JCP = 1.88, CH). Anal. calcd for C36H30AlNP2: C, 76.44; H,
5.35; N, 2.48. Found: C, 76.03; H, 5.09; N, 2.37.
Synthesis of [iPr-PNP]AlH2 (6b). Colorless crystals sui-
table for X-ray diffraction analysis were grown by layering
pentane on a concentrated diethyl ether solution at -35 °C.
Yield: 83%. 1H NMR (C6D6, 500 MHz): δ 7.40 (dd, 2, J = 3 and
8, Ar), 7.07 (t, 2, Ar), 7.04 (m, 2, Ar), 6.75 (t, 2, J = 7.5, Ar), 4.93
(br s, 2, Δν1/2 = 35, AlH), 2.07 (m, 2, CHMe2), 1.84 (m, 2,
CHMe2), 1.21 (dd, 6, CHMe2), 1.12 (dd, 6, CHMe2), 1.08 (dd, 6,
CHMe2), 0.85 (dd, 6, CHMe2). 31P {1H} NMR (C6D6, 202.31
MHz): δ -20.64. 13C {1H} NMR (C6D6, 125.5 MHz): δ 160.47
(t, JCP = 9.54, C), 133.60 (s, CH), 131.59 (s, CH), 120.15
(s, CH), 119.53 (s, CH), 117.69 (t, JCP = 11.92, C), 23.09
(s, CHMe2), 20.12 (t, JCP = 5.02, CHMe2), 19.70 (t, JCP
2.76, CHMe2), 19.33 (t, JCP = 5.90, CHMe2), 19.03 (t, JCP
3.26, CHMe2), 16.78 (t, JCP = 1.88, CHMe2). Anal. calcd for
C24H38AlNP2: C, 67.10; H, 8.92; N, 3.26. Found: C, 66.60; H,
8.13; N, 3.78.
=
=
Catalytic 1-Hexene Polymerization. A chlorobenzene
solution (0.25 mL) of B(C6F5)3 (2.5 μmol) was added to a
1-hexene solution (2 g) of 2 (2.625 μmol) at room temperature.
The reaction was stirred at room temperature for 30 min and
quenched with MeOH (ca. 1 mL). All volatiles were removed
under reduced pressure (ca. 100 mTorr at 70 °C) until the
product weight remained constant.
Synthesis of [Ph-PNP-iPr]AlH2 (6c). Yield: 87%. The
dichloride 5c could be alternatively prepared in situ by the
addition of 1 equiv of MeAlCl2 to 1c in toluene at -35 °C.
1H NMR (C6D6, 500 MHz): δ 7.68 (m, 2, Ar), 7.65 (m, 2, Ar),
7.35 (dd, 1, Ar), 7.23 (dd, 1, Ar), 7.15 (m, 1, Ar), 7.05 (td, 1, Ar),
7.00 (m, 4, Ar), 6.94 (m, 4, Ar), 6.66 (dt, 2, Ar), 5.25 (br s, 2,
Δν1/2 = 80, AlH), 2.03 (m, 1, CHMe2), 1.85 (m, 1, CHMe2), 1.15
(dd, 3, CHMe2), 1.11 (dd, 3, CHMe2), 1.07 (dd, 3, CHMe2), 0.84
(dd, 3, CHMe2). 31P{1H} NMR (C6D6, 202.31 MHz): δ -17.19
Acknowledgment. We thank the National Science Council
of Taiwan for financial support (NSC 96-2628-M-110-007-MY3
and 96-2918-I-110-011), Ms. Mei-Hui Huang for a preli-
minary study, Mr. Ting-Shen Kuo (at NTNU) for assistance
with X-ray crystallography, and the National Center for High-
Performance Computing (NCHC) for computer time and
facilities.
(d, 1, 2JPP = 49.97, PiPr2), -28.54 (d, 1, 2JPP = 49.97, PPh2). 13
C
{1H} NMR (C6D6, 125.5 MHz): δ 160.68 (d, JCP = 17.32, C),
159.08 (d, JCP = 22.84, C), 135.06 (s, CH), 134.46 (d, JCP =
Supporting Information Available: X-ray crystallographic
data in CIF format for 2a-c, 3b-c, 5b, and 6b. This material
is available free of charge via the Internet at http://pubs.acs.org.
14.68, CH), 134.26 (d, JCP = 12.80, CH), 133.41 (d, JCP =
16.44, C), 133.28 (s, CH), 132.04 (s, CH), 131.98 (s, CH), 131.85
(s, C), 130.30 (s, CH), 129.77 (s, CH), 129.19 (d, JCP = 32.12,